A tube-forming machine and process has a supply for delivering an elongate, folded, plastic web (10) along a path of travel. The web may be clear polyethylene folded treated surface to treated surface. A cutting mechanism (14) is positioned along the path including a hard cylindrical roll (18) and a cutter (24) having a cutting head and means to bias the head toward the roll. A rotatable sealing drum (15) has a cylindrical web engaging surface delineating a further portion of the path. A set of circumferentially spaced flame-emitting nozzles (55) are positioned adjacent the drum surface section. Each of the nozzles includes a tip disposed within the cylinder delineated by said drum surface and has an axis disposed in an imaginary radial plane. Each tip is directed radially upwardly to impinge its flame against portions of a web being fed along the path when such portions project from said drum surface. Each tip axis is at an angle from 90° to 60° with an imaginary line located by the intersection of such imaginary plane with said drum surface section with the 60° orientation of the tip axis being canted toward the drum. Preferably each tip axis is canted toward the drum at an angle of from 65° to 68° with said imaginary line.